Torpedo propulsion and control



Aug. 21, 1962 B. w. MCCORMICK ET AL 3,050,024

TORPEDO PROPULSION AND CONTROL Filed June 26, 1957 3 Sheets-Sheet 1 FIG. 1

BARNES W. MCORMICK JOSEPH J. EISENHUTH GEORGE F. WISL/CENUS IN VEN TOR.5

Aug. 21, 1962 B. w. MCCORMICK ET AL 3,050,024

TORPEDO PROPULSION AND CONTROL Filed June 26, 1957 3 Sheets-Sheet 2 BARNES W. MCORM/CK JOSEPH J. E/SENHUTH GEORGE F. W/SL/CENUS IN VEN TORS BY I Z6 7 4 AT ORNEYS FIG. 3

Aug. 21, 1962 B. w. MCCORMICK ET AL 3,050,024

TORPEDO PROPULSION AND CONTROL Filed June 26, 1957 3 Sheets-Sheet 3 O Propeller "25 FIG. 8

BARNES W. MCORM/CK JOSEPH J. E/SENHUTH GEORGE F. WISLICENUS IN VEN TORS ArroR/vEys United States Patent @fifice 3,050,024 Patented Aug. 21, 1962 3,050,024 TORPEDO PROPULSION AND CONTROL Barnes W. McCormick, Springfield, and Joseph J. Eisenhuth and George F. Wislicenus, State College, Pa., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed June 26, 1957, Ser. No. 668,267 6 Claims. (Cl. 114-20) This invention relates generally to torpedoes and more particularly to propellers and stabilizer surfaces for a torpedo. As used herein, stabilizer surfaces have reference to the fixed means utilized to render a torpedo stable during travel which generally also contains movable control surfaces for controlling or changing the direction of travel of the torpedo,

The concept of propelling torpedoes and maintaining them stable in travel has remained unchanged almost from the date of the first practical torpedo. This concept generally includes a long cylindrical body having a tapered rearward portion provided with a propeller at the most rearward point and usually four fixed stabilizer surfaces extending outwardly at right angles just forward of the propeller. The prior art is replete with innovations of the basic concept, but for both practical and technical reasons few, if any, have as yet ever met with substantial success or come into Widespread use. Further, the abovementioned innovations have almost without exception been concerned with providing increased power, increased efficiency, increased stabilization, increased maneuverability and the like.

It was not until recently that designers of torpedoes became interested in the noise generated by the torpedo during travel and this has led to a considerable interest in the phenomenon of cavitation. However, so far as is known, heretofore all such efforts to reduce noise with regard to cavitation have not met with substantial success or come into practical use, especially with regard to the development of a hydrodynamically stable torpedo that is fast, that produces a minimum of noise and that can be launched in accordance with conventional methods.

It is, therefore, a principal object of this invention to provide a propeller and stabilizer surfaces for a torpedo that result in improved torpedo performance.

Another object of this invention is to provide a propeller and stabilizer surfaces for a torpedo having improved cavitational characteristics.

A further object of this invention is to provide new and novel stabilizer surfaces for a torpedo that cooperates with the propeller in a new and novel fashion.

A still further object of this invention is the provision of a propeller and stabilizer surface arrangement that will etficiently propel a torpedo by means of a single propeller while maintaining a zero net torque and that will be less susceptible to cavitation and will be more effective in controlling the torpedo.

Another object of the invention is the provision and location of new and novel stabilizer surfaces for a torpedo that are less susceptible to cavitation and that allow the use of propellers having improved cavitation characteristics.

These and other objects and features of the invention, together with their incident advantages, will be more readily understood and appreciated from the following detailed description and the drawings which illustrate an embodiment of the invention in which:

FIGURE 1 is a perspective view of the rear portion of a torpedo incorporating the present invention.

FIGURE 2 is a fragmentary side elevation partially in section of one fin mounted on a hub and showing the location of various stations on the fin.

FIGURE 3 is a diagrammatic representation showing in cross-section each station indicated in FIGURE 2 and showing the disposition and configuration of the cross section of each station with relation to the cross section of each other station, a hypothetical stack-up line which passes through each cross-section, the angle at which each cross-section is disposed with reference to the longitudinal axis of the torpedo and the camber of each cross section.

FIGURE 4 is a front elevation of one fin showing in particular the twist or skew in the leading edge of the fin.

FIGURE 5 is a rear elevation of the fin shown in FIG- URE 4 and shows in particular the twist or skew in the trailing edge of the fin.

FIGURE 6 is a fragmentary side elevation partially in section of a propeller and fin combination in accordance with the invention and showing the intersection of the streamline with the propeller and fin at mid-chord radii of respectively r and r FIGURE 7 shows the relation of the cross section of the propeller at the radius r to the cross section of the fin at the radius r, shown in FIGURE 6 and also shows velocity diagrams for the streamline of FIGURE 6 at these respective radii, the velocity diagram at the radius r being shown adjacent the propeller cross section and the velocity diagram at the radius r being shown adjacent the fin cross section.

FIGURE 8 is a velocity diagram at the quarter chord line of a fin constructed and formed in accordance with the invention.

FIGURE 1 shows the rear portion 15 of a torpedo of conventional design having a substantially smooth outer surface 16 over its entire length and provided with a propeller 17 attached to its rearmost portion and adapted to propel the torpedo in a forwardly direction by con ventional means such as for example, an electric propulsion motor, propeller shaft and associated components (not shown.) Disposed rearwardly of the propeller 17 and affixed to the rear portion 15 of the torpedo in nonrotatable relationship therewith are a plurality of stabilizers or fins 18 (in this case, eight) integrally mounted on a hub 19 the exposed outer surface of which forms a continuation of the rear portion 15 of the torpedo and the propeller hub 21. As best shown in FIGURE 2' and by way of example, the hub for the stabilizers may be removably attached to the torpedo by means of a rigid shaft 22 non-rotatably disposed within a hollow propeller shaft 23 and a bolt 24 adapted for threaded engagement with the rigid shaft 22 or the like and provided with a conical rear portion 25.

For the number of fins shown in FIGURE 1 the hub 19 for the stabilizers is preferably formed separately and the root section 26 of each completed fin 18 permanently attached thereto as by welding or the like. In the preferred embodiment as shown in FIGURE 1 each fin 18 extends radially to about the diameter of the torpedo and the leading edges 27 of each stabilizer surface or fin 18 is disposed about within one fin chord length of the rearmost trailing edge 28 of the propeller 17.

As shown in FIGURE 2 and FIGURE 3 each fin 18 has a plurality of stations designated respectively A, B, C, D, E, F and G wherein the radial cross section of each stabilizer surface or fin 18 at each different station is disposed at a specific and individual angle to the longitudinal axis of the torpedo (represented by lines 33 in FIGURE 3) and has a specific camber the determination of which is described hereinafter. By reference to and inspection of FIGURE 2 and FIGURE 3 it can readily be seen that each stabilizer surface or fin 18 has an individual stack-up line 31 passing through different points in the cross sections of each different fin at each station and that each fin is respectively twisted or skewed the same amount and in the same manner about its stack-up line 31 such that the leading edge 27 of each fin forms an arcuate surface both in a longitudinal and radial direction as shown in FIGURE 4 and such that the trailing edge 32 of each fin forms an entirely different arcuate edge as shown in FIGURE 5 as and for the purposes described hereinbelow.

In order to fully describe the construction and operation of the fins 18 reference is now made to FIGURES 6 through 8 of the drawings as an aid in the description of the manner employed in formulating the fins and to fully describe their unique configuration.

The preferred ermbodiment of the present invention contemplates the operation of a normally fixed set of stabilizer surfaces or fins immediately behind a given single propeller, that the stabilizer surfaces or fins satisfy the stability requirements of the torpedo, that they produce a net torque equal and opposite to that produced by the propeller and that they have a cavitation performance at least as good as that of the propeller. Since the con figuration of each 'fin is substantially identical with every other fin, reference is made hereinbelow in substance to the design of a single fin.

In the following discussion let:

r =radius at which streamline passes through the fins at midchord r radius at which streamline passes through the propeller at midchord r =hub radius of propeller r =hub radius of fin R =propeller radius w=rotational speed in radians per second w =tangen=tial velocity induced by propeller w =axial velocity induced by propeller w =induced velocity of the fin section w =velocity induced by the fins at the quarter chord-line F :Prandtls tip loss factor k=spacing factor giving change of w with axial distance B number of propeller blades B number of fins F bound circulation of fins I =bound circulation of propeller blade =fiuid mass density Q =torque produced by the propeller Q =torque produced by the stabilizer surfaces l3=propeller blade section angle fi =angle from transverse plane to zero lift line of a fin section fi =angle from transverse plane to a tangent of the mean camber line at the quarter chord point l =distance of fin from the torpedo center of gravity for new design l' =distance of fin from the torpedo center of gravity for existing torpedo V'=inflow velocity at stabilizer surface of existing torpedo C =fin section chord of new design C',=fin section chord of existing design R =fin radius of existing design r =hub radius of fin for existing design In the design of fins as contemplated by the present invention stability requirements involve the choice of a fin planform with sufficient area to stabilize the torpedo. In the preferred embodiment the total fin height is restricted to the diameter of the torpedo, hence the area is therefore dependent on the choice of the radial chord distribution and should be such as will meet the stability needs of the torpedo. It has been found through experience that Equation 1 as given hereinbelow may be used for finding the necessary chord distribution for replacing conventional stabilizer surfaces and consequently allowing a determination of chord distribution. If the new fin or fins are being designed to replace conventional stabilizer surfaces disposed and mounted forwardly of the propeller substantially the same degree of stability will be maintained if the following is held true:

The remaining restrictions on the chord distribution are those imposed by fin cavitation performance as will be more thoroughly discussed hereinbelow.

The design of the fin for torque cancellation requires the determination of the radial distribution of bound circulation I that will be needed for torque cancellation. With reference now to the propeller-fin combination 34-35 as shown in FIGURE 6 and which is merely representative, it will be noted that the streamline 36 which passes through the propeller 34 at midchord at a radius of r intersects the fin 35 at midchord at a radius of r A representative velocity diagram for the streamline 36 relative to the propeller section at radius r and the fin section at radius r is shown in FIGURE 7. Because of the magnitude of the angles involved the assumption may be made that the induced velocity w of the fin section lies in a transverse plane as shown in FIGURE 7 and therefore has no axial component. The r having the same inflow as that at r may be calculated from continuity considerations as r=\ ph fl? For best operation and especially for good cavitation performance the stabilizer surface or fins must be designed to operate with a specific propeller or type of propeller, hence from the design of such a propeller induced velocities of the propeller will be known and the following expression, for torque of the propeller not including profile losses, can be written:

R QD=BDP T Jami wear. (3)

D The torque of the fins corresponding to the velocity diagram shown in FIGURE 7 can also be written, again neglecting profile losses, as:

Initially, it may be convenient to cancel torques locally. Therefore, again from continuity considerations, where r dr =r dr Equations 3 and 4 lead to the expression:

Since as already mentioned, the fins are preferably designed to extend to substantially the maximum radius of the torpedo, it is important from the point of view of cavitation to extend loading of the fins over the full radius of each fin. For this reason it is preferable to first calculate I from Equation 6 and then to modify this I} to extend out to the full radius of the fins, maintaining the same total torque but leaving unchanged the 1; near the hub for the purpose of minimizing the possibility of a cavitating hub vortex.

Once the radial distribution of I} for torque cancellation has been established the physical configuration of the sections, i.e., the fin section angles, the fin section cambers, and the like may be determined in the following manner. The ideal approach for the design of each fin would be to use an exact lifting surface theory for a fin in a rotational inflow. Such a formulation is, however, an imposing one. Also, no readily usable factors are available such as Prandtls tip loss factor or Goldsteins K factor used in propeller design whereby the circulation may be related to the induced velocity at each section as a function of the relative radius, angle of inflow and the number of fins involved. An acceptable approach, the validity of which has been proven by experience, is to use Weissingers lifting surface approximation for wings described in The Lift Distribution of Swept-Back Wings, 1'. Weissinger, N-ACA TM. No. 1120, March 1947, which accounts for the rotational inflow only as a non-uniformity in the inflow velocity. Weissingers so-called L-rnethod states in substance that for a given lifting surface, if the bound circulation is assumed to be located at the quarter-chord line, then the distribution of the bound circulation must be such that the resulting flow is tangent to the surface at the three-quarter chord line. This is equivalent to the statement that the angle of the resultant velocity at the three-quarter chord point must be the same as the angle of the zero lift line. This angle, and hence the angle for each section, may be established by determining w at each station or alternately, from the geometry of FIGURE 7 and by use of the formula:

The determination of the values of W: is most conveniently accomplished by the use of an electromagnetic analogy. The analogy that may be utilized is that of substituting the magnetic field about a conducting wire for the induced velocity field about a vortex. In the analogy referred to hereinabove a common wire representing the bound vortex is located at the quarter-chord line and to it are attached other closely spaced wires representing the trailing vortex system. A source of alternating potential is connected to these wires and is distributed in such a manner that the span-wise distribution of current in the bound vortex wire is proportional to the span-wise distribution of P By measuring the induced voltages at the three-quarter chord point these voltages may be translated into induced velocities. The effect of numbers of blades may be obtained by again taking measurements at the relative positions of other fins at the three-quarter chord points. By adding the results the effect of the entire system of fins may be obtained.

The analogy and use thereof referred to hereinabove is thoroughly discussed and described in Development of Electromagnetic Analogy for Computation of Induced Propeller Velocities, a thesis by Barnes W. McCormick, Jr., published 1949, the Pennsylvania State University, to which reference is made. The determination of w such as for example in the manner described immediately hereinabove allows the determination of the direction of the zero lift line of each station along the fin. The determination of the angle of zero lift for each station allows the determination of the proper cambers and section angles on the basis that, for good cavitation performance all of the lift of the sections must be obtained from camber rather than by any angle of attack. The proper determ nation of camber requires that the camber of the sections be determined on the basis of the stipulation that the resultant velocity at the quarter-chord line be tangent to the mean camber line at that point for the reason that determination of the zero lift line and the slope of the lift curve of a section is not sufiicient for the calculation of a lift coefficient, and hence, the camber of the section since the velocity that must be used as a reference for the angle of attack is not clearly defined. As noted immediately hereinabove the determination of the resultant velocity is dependent on finding the induced velocity Wf 25 at the quarter-chord point as shown in FIGURE 8 which induced velocity may be found by integrating Biot-Savart equations or by use of the electromagnetic analogy, reference to which has been made hereinabove. The angle of the resultant velocity may be determined from the formula:

V-l-kFun (8) l t-25 =taIF1 camber, the geometry and orientation of each section is satisfied by finding the camber which will satisfy Equations 7 and 8, simultaneously. The choice of thickness distribution if desired may be based on mechanical considerations rather than on hydrodynamic considerations.

Certain aspects of improving the cavitation performance of the fins have already been mentioned hereinabove. For instance, it was noted that the chord distribution must meet the requirements necessary for good cavitation performance. One of the ways in which cavitation performance may be improved is to increase the fin or force producing area so that the cambers required and consequently the magnitude of the minimum pressures are reduced for the individual hydrofoil sections. One of the controls available for fin area is the distribution of chord along each fin, hence increasing the chord lengths will improve the cavitation performance. Further, the total fin area may also be increased by increasing the number of fins to allow a reduction of the loading on each fin and thereby improve cavitation performance.

Still further, as mentioned hereinbefore, the choice for the 1} distribution is another control that may be used to improve cavitation performance. By redistributing I} to be substantially constant over the majority of the length of the fin no particular section will be overloaded and con-sequently will have no accompanying poor cavitation performance. Further, the maintaining of 1} equal to the propeller I near the hub reduces the possibility of hub vortex cavitation. Still further, the gradual decreasing of I near the tips of the fins reduces the possibility of tip vortex cavitation.

As noted hereinabove all the lift of the sections is obtained by camber alone thereby allowing a substantially constant chord-wise distribution of pressure to be maintained at the sections and it is the presence of such a distribution that prevents the existence of low pressure cavitation producing regions. NACA Series 16 sections which have the flat pressure distribution just mentioned for zero or very low angles of attack have been used in practice with satisfactory results and may be used if desired.

The provision of stabilizer surfaces designed to operate in combination with a propeller (as shown and described herein), thereby allowing the propeller to be designed for operation on a clean torpedo body of specific design, has shown that the index of cavitation for both the propeller and stabilizer surfaces on such a torpedo may be reduced over that presently existing with regard to prior practices by as much as a factor of four or five and at the very least a cavitation index may be secured that is generally not obtainable with prior art practices under even the most ideal conditions.

It will be readily appreciated that in the arrangement and development illustrated in the drawings and described by way of example hereinabove may be varied and modified according to requirements. As may be apparent latitude is available in the design of the fins with regard to fin area, fin length, number of fins and section camber and section angles and the like since they are generally interdependent, the modification of one being compensated by or allowing modification of another to a greater or lesser extent. Moreover, the present invention is not necessarily limited to a single propeller application, although such is believed preferable, and may be adapted for steering a torpedo.

It is, therefore, to be understood that while the present invention has been described in its preferred embodiment, it is realized that modifications may be made, and it is desired that it be understood that no limitations upon the invention are intended other than what may be imposed by the scope of the appended claims.

What is claimed as new and desired to secure by Letters Patent of the United States is:

1. Stabilizing means for a torpedo having propulsion means including a propeller at its rearward end comprising: a non-rotatable hub element disposed rearwardly of the propeller and on the longitudinal axis of the torpedo; means connecting said hub element to the torpedo; and a plurality of fins radially carried by said hub and having a plurality of diiferent stations, said fins having a predetermined angle and camber for each said diiferent station determined by the propeller water exit conditions at each said different station, said angles and said camber creating a net torque equal and opposite to that created by the propeller in operation and reducing the magnitude of low pressure areas on the fins.

2. Stabilizing means for a torpedo having propulsion means including a propeller at its rearward end comprising: a non-rotatable hub element disposed rearwardly of the propeller in close proximity thereto and on the longitudinal axis of the torpedo; means connecting said hub element to the torpedo; and a plurality of fins radially carried by said hub and having a plurality of different stations, each said station having an airfoil cross section disposed at a predetermined angle to the flow of water from the propeller at each said station, each said difierent station additionally having a predetermined camber for producing a torque opposite to that created by the propeller in operation, the net torque produced by the fins being substantially equal and opposite to that created by the propeller, the said angle of each said station substantially reducing the formation of low pressure areas over substantially the entire surface of each said fin.

3. The combination as described in claim 2 wherein the camber of each diiferent station is selected such that the resultant water velocity at the one-quarter chord line is tangent to the mean camber line at that point.

4. Stabilizing means for a torpedo having propulsion means including a propeller at its rearward end having an inner portion and a predetermined load characteristic comprising: a non-rotatable hub element disposed rearwardly of the propeller and on the longitudinal axis of the torpedo; means connecting said hub element to the torpedo; and a plurality of fins radially carried by said hub, each said fin having an inner portion, a middle portion and an outer portion, said fin inner portion having a load characteristic substantially the same as the load characteristic of the inner portion of the propeller, said 0 fin middle portion having a substantially flat load characteristic less than the maximum load characteristic of the propeller, said fin outer portion having a load characteristic that decreases in an outwardly radial direction, each of said fins having a plurality of radially disposed difierent stations, said fins having a predetermined angle and camber for each said difierent station determined by the propeller water exit conditions at each said different station cooperating to produce a net torque equal and opposite to that created by the propeller in operation and reduce the magnitude of low pressure areas on the fins.

5. The combination as described in claim 4 wherein there is provided a minimum number of said fins such that the projected area of said fins in any one plane is sutficient to maintain stability.

6. In a torpedo having a substantially smooth outer surface and propulsion means including a propeller at its rearward end the combination comprising: a propeller, said propeller being designed for operation with said smooth torpedo body; a non-rotatable hub element disposed rearwardly of the propeller in close proximity thereto and on the longitudinal axis of the torpedo; means connecting said hub element to the torpedo; and a plurality of fins radially carried by said hub and having a plurality of different stations, each said station having an airfoil cross section disposed at a predetermined angle to the flow of water from the propeller at each said station, each said different station additionally having a predetermined camber for producing a torque opposite to that created by the propeller in operation, the net torque produced by the fins being substantially equal and opposite to that created by the propeller, the said angle of each said station substantially reducing the formation of low pressure areas over the entire surface of each said fin.

References Cited in the file of this patent UNITED STATES PATENTS 2,355,413 Bloomberg Aug. 8, 1944 2,746,672 Doll et a1. May 22, 1956 2,795,394 Slivka et al June 11, 1957 2,798,661 Willenbrock et al. July 9, 1957 a" at w Aw 

